Organolithium initiated polymerization



United States Patent 3,335,122 ORGANOLITHIUM INITIATED POLYMERIZATION William J. Trepka, Bartlesville, Okla., assignor to Phillips Petroleum Compan a corporation of Delaware No Drawing. Filed Apr. 20, 1964, Ser. No. 361,219 Claims. (Cl. 260--94.2)

This invention relates to an improved organolithium polymerization initiator and to the method for making same. In another aspect it relates to a polymerization of vinylidene-containing monomers with a novel organolithium initiator.

Monomers containing vinylidene groups such as conjugated dienes and vinyl-substituted aromatic compounds are readily polymerized with organolithium compounds such as butyllithium. Polymers which are terminally reactive can be formed by using such an initiator and terminat ing the polymerization with a reagent or reagents so that the lithium atoms present in the polymer are replaced with stable reactive groups. The polymerization reactions proceed to completion in many instances with substantially quantitative production of polymer from the momomers charged, and the molecular weight of the polymer can be regulated to some extent by varying the amount of initiator used. Increasing the concentration of initiator in relation to the monomer charged reduces the molecular weight of the product. In this manner liquid, semi-solid and solid polymers can be prepared.

In following a procedure as above described, controlling the molecular weight is difiicult when preparing rubbery polymers or solid resins of high molecular weight. Very small amounts of initiator of the type described are required to produce solid polymers so that accurate regulation of initiator level is diflicult. It is desirable, therefore, to find methods of increasing the inherent viscosity of polymers while operating at controllable initiator levels.

I have discovered that a polymerization initiator which is valuable for polymerizing vinylidene-con-taining monomers can be prepared by reacting an alkyllithiumm compound with a benzyl alcohol or a hydrocarbon-substituted derivative thereof. The reaction product formed by contacting these materials has limited solubility in hydrocarbon solvents and thereby permits more accurate regulation of the inherent viscosity of the polymer formed in a hydrocarbon medium.

It is an object of my invention to provide an improved method for polymerizing vinylidene-containing monomers. Another object is to provide a method for preparing an organolitihum initiator which is sparingly soluble in hydrocarbon solvent. Another object is to provide a polymerization initiator which can be used to polymerize conjugated dienes, such as isoprene or butadiene, in a hydrocarbon solvent to form solid, rubbery polymers having higher inherent viscosity than would be obtained using the same initiator level of an alkyllithium compound. Other objects, advantages and features of my invention will be apparent to those skilled in the art from the following discussion.

The initiators of this invention are made by reacting together an alkyllithium compound and a benzyl alcohol. The alkyl group of the alkyllithium compound preferably contains no more than 12 carbon atoms. Examples of such materials which are suitable include ethyllithium, n-butyllithium, n-hexyllithium, n-dodecyllithium, and the like. The lower alkyllithium derivatives of 2 to 6 carbon atoms are preferred.

The benzyl alcohol compound used in the initiator preparation is represented by the formula:

ice

wherein R is a saturated aliphatic or cycloaliphatic radical and m is an integer of 0 to 4 with the total number of carbon atoms in the R groups not exceeding 6. At least one of the positions ortho to the CH OH group should be unsubstituted. Examples of such compounds include benzyl alcohol, 4-methylbenzyl alcohol, 2,4-diethylbenzyl alcohol, 3-cyclopentylbenzyl alcohol, 3,5-diisopropylbenzyl alcohol, 2,3,4,5-tetramethylbermyl alcohol, 3-methyl- S-n-amylbenzyl alcohol, 4-cyclohexylbenzyl alcohol, and the like.

The initiators are prepared by reacting the benzyl alcohol compound with the alkyllithium in a hydrocarbon diluent. The reaction can be carried out at room temperature but elevated temperatures are preferred, generally in the range of about to 200 F. The reaction mixture should be well agitated. The amount of alkyllithium should be at least stoichiometric and preferably is used in excess. Normally from 2 to 10 moles, and preferably from 3 to 5 moles, of alkyllithium are employed per mole of benzyl alcohol compound.

Suitable hydrocarbon diluents include benzene, toluene, cyclohexane, methylcyclohexane, xylene, n-butane, n-hexane, n-heptane, isooctane, n-dodecane, and similar paraflins, cycloparafiins and aromatics, ordinarily containing about 4 to 10 carbon atoms per molecule. The time required for the preparation of the initiator can vary from a few minutes to several hours, depending upon the conditions and the reactants. As the initiator is formed, being only sparingly soluble in the diluent, it precipitates and can be separated from the reaction medium by any suitable means, such as centrifugation or filtration. This removes unreacted materials and side products and the solid initiator can be washed further and then redispersed in a hydrocarbon.

The vinylidene-containing monomers which can be polymerized by the initiators described herein are preferably the conjugated dienes containing 4 to 12 carbon atoms per molecule and those containing 4 to 8 carbon atoms are more highly preferred. Examples of such conjugated dienes include 1,3-butadiene isoprene, 2,3-dimethyl-1,3 butadiene, piperylene, 3 butyl-l,3 octadiene, 2- phenyl-1,3-butadiene and the like. Conjugated dienes containing halogen and alkoxy substituents such as chloroprene and 2-methoxy-l,3-butadiene can also be used. The conjugated dienes can be formed into homopolymers or copolymers including block copolymers prepared by charging the monomers sequentially.

Also included among the vinylidene-containing monomers are the vinyl-substituted aromatic compounds such as styrene, l-vinylnaphthalene, 2-vinylnaphthalene and the alkyl, cycloalkyl, aryl, alkaryl, aralkyl, alkoxy, aryloxy, and dialkyla'mino derivatives thereof in which the total number of the carbon atoms in the combined substituents does not exceed 12. Examples include S-methylstyrene, 4-dodecylstyrene, 4-cyclohexylstyrene, 2-ethyl-4- benzylstyrene, 4-methoxystyrene, 4-dimethylamin0styrene, 3,5-diphenoxystyrene, 4-p-tolylstyrene, 4-phenylstyrene, 4,S-dimethyl-l-vinylnaphthalene, 3-n-propyl-2-vinylnaphthalene, and the like. These vinyl-substituted aromatic trogen. Examples are the pyridine, quinoline or isoquinoline derivatives corresponding to those described in connection with the vinyl-substituted aromatic compounds. Examples include 2-vinylpyridine, S-cyclohexyl-Z-vinylpyridine, 6-methoxy-2-vinylpyridine, 3-benzyl-4-vinylpyridine, 4-phenyl-2-vinylpyridine, 4-dimethylamino-2-vinylquinoline, 3-vinylisoquinoline and the like. Other polar monomers include methyl acrylate, ethyl acrylate, methyl methacrylate, butyl methacrylate, acrylonitrile, methacrylonitrile, N,N-dimethylacrylamide, and similar acrylic and alkacrylic acid esters, nitriles and N,N-disubstituted amides. Vinylfuran and N-vinylcarbazole can also be used.

The polymerizations are carried out in predominantly hydrocarbon liquid diluents at temperatures in the range of=about 100 to +150" C., preferably between 75 and +75 C. The most desirable temperature depends upon the monomers and the initiator used in the polymerization. The amount of initiator charged can vary considerably because of its limited solubility but ordinarily the amount used is in the range of about 0.5 to 200, preferably 1 to 150 milliequivalents per 100 grams of monomers. The-milliequivalents of initiator used in the polymerizations is based upon the total lithium present in the initiator composition as determined by titration or by calculation from the molarity, knowing the number of lithium atoms in each molecule of initiator.

The initiator can be titrated by hydrolyzing a sample of the product with water and then titrating the lithium with'HCl. The polymerization diluent issuitably a hydrocarbon of the same type previously described for preparation of the initiator.

The polymerization mixture should be agitated and the reaction time can extend from a few minutes to 100 hours or more. Usually a short induction period is required but in the time allowed for the polymerization the conversions can be expected to be nearly quantitative. At the end of the reaction the initiator can be inactivated and the polymer coagulated by adding an acid or alcohol. The polymer is then. separated, washed and dried using conventional recovery techniques.

In order to introduce functional groups in the polymer in place of the lithium atoms, it is necessary to treat the polymer solution before inactivating the initiator with water, alcohol or acid. The polymer solution can be treated with carbon dioxide to introduce carboxy groups, with a cyclic disulfide or sulfur to introduce mercapto groups,

with aldehydes, ketones or epoxy compounds such as acetaldehyde, acetone or ethylene oxide to introduce hydroxy groups, with carbon disulfide to introduce carbodithio groups, and the like. It is ordinarily necessary to remove the lithium atoms from the salt which forms in the termination reaction by hydrolysis using alcohol, acid or water.

4 a polymer containing terminal hydroxy groups or a polyaziridinyl compound to couple a carboxy terminated polymer.

The following examples are presented as illustrative of the invention. It is not intended, however, that the invention should be limited thereto.

EXAMPLE I A polymerization initiator was prepared by reacting n-butyllithium with benzyl alcohol. The following recipe was employed:

Benzyl alcohol, mole 0.025 n-Butyllithium, mole 0.0 83 Toluene (100 ml.), mole 0.94 Time, hours 192 Temperature, F. 122

Toluene was charged to the reactor'after which it was purged with nitrogen. Benzyl alcohol was then added, the mixture was cooled to ice bath temperature, and the hutyllithium was charged. The temperature was increased to 122v F. and the reactants were agitated for 192 hours. The liquid mixture was centrifuged to separate the solid reaction product. The supernatant liquid was discarded, the precipitate was washed once with toluene and then with n-pentane to remove unreacted butyllithium. The washings were discarded and the solid product was dispersed in n-pentane. Total volume of the final, dispersion was milliliters. It had a normality of 0.48. Total alkalinity of the dispersion expressed as equivalents of lithium was 0.082.

The reaction .product of butyllithium was benzyl alco- 1101 was employed as the initiator for the polymerization of isoprene. A series of runs was made using variable amounts of initiator. The recipe was as follows:

Isoprene, part by weight 100 n-Pentane, parts by weight 1000 Initiator, milliequivalents Variable Time, hours 24 Temperature, F. 122

The diluent was charged first, the reactor was then purged with nitrogen, and isoprene was added. The initiator was introduced last. The reactants were agitated throughout the polymerization period. At theclose of the polymerizations the reactions were terminated by the addition of an isopropyl alcohol solution of 2,2-methylene-bis(4-methyl-6-tert-butylphenol), the amount used being suflicient to provide one part by weight of the antioxidant per 100 parts of rubber. The polymers were co agulated with isopropyl alcohol, separated, and dried. Microstructure, inherent viscosity, and gel were determined on each of the products. The results are summarized in the following table.

I Milliequivalents per 100 grams monomer. 2 Raw values.

The polymer can be coupled while it still contains an active terminal lithium atom by selection of the type and The above data show that polymers having. high inherent viscosity can be formedat controllableinitiator amount of terminating agent used. F exa l carbon 70 levels. A corresponding. amount of butyllithium, used as iioxide, depending upon the amount used, can either :ouple the polymer or terminate it with carboxy groups. Also the polymer containing terminal reactive groups :an 'be coupled by reaction with a polyfunctional compound. For example, a diisocyanate can be used to couple the initiator would produce a polymer of considerablylower molecular weight.

EXAMPLE II A polyisoprene prepared as described in Example I with an initiator level of 4.4 milliequivalents per 5 grams of isoprene and having a cis-content of 84.2 percent and a Mooney value (ML-4 at 212 F.) of 62.0 was evaluated in a treadstock recipe. Mixing was done in a Midget Banbury. Processing was good and adequate break- 6 Toluene (400 nil.), moles 3.8 Time, hours 192 Temperature, F 122 The procedure was the same as described in Example down of the rubber was achieved in a single mixing cycle 5 (6 minutes) at 290 F. The compounding recipe, data on E total the dlspilrslon f the processing properties, and properties of the vulcanized e 8 exliressef i 1 icnts o 3%; stock are presented in the following table: 11 y orma 0 t e q P e This dispersion was employed as the initiator in a series Compounding Tempe, Parts y welght of runs for the polymerization of butadiene. The followpolymer 00 ing recipe was used: H abfaslon furnace black u 1,3-butadiene, parts by weight 100 Zinc 9 3 Cyclohexane, parts by weight 780 Steam: Initiator, milliequivalents Variable Flexamine 1 Time hours 24 Flexzone 3C 2 T "e u em erature, F 122 Aromatic oil (Philrich 5) 5 P Pepton 22 3 1 Procedure for polymerization and recovery of the poly- Sulfur 2.25 mers was the same as in Example I. Results are sum- NOBS Special 0.5 marized in the following table:

Microstructrue, percent Run Initiator, Conversion Inherent Gel, No. meq./hrn. percent Viscosity percent Cis Trans Vinyl 5 100 50. 2 a4. 2 5. 6 e. 34 0 3 100 83.5 21. 9 4. 6 9.15 0 2.8 100 75. 5 20. 7 a. s 9.69 0 2. 6 100 78. 0 17. 9 4.1 10. G6 0 Processing properties The above data show the reaction product of n-butylcompounded at F 31.8 lithium and benzyl alcohol is an effective in tiator for D polymerization of butadiene and that the initiator level Extrusion at 195 F.. b f 1 Inches/minute 665 can e varied wit in a convenient range to orm p0 yl tvel hi hinhere tviscosit G 121 mers of re a i y g n y.

rams minute Ratin (Garve die) 4O Attempts to prepare polymerization initiators by reactg y ing an alkyllithium with benzylamine and 'benzylmercap- Physical properties d minutes at 293 F tan was not successful as no precipitate formed as in the case with benzyl alcohol. X moles/C65? In the above examples, microstructure, inherent vis- 9 modulus, P- 1290 cosity and gel were determined for the polymers accord- Tensllei' P- 2990 ing to the following procedures: g P 540 Microstructures were determined with a commercial tenslle at 200 P- 1385 infrared spectrometer. For polyisoprene the samples were F37 dissolved in carbon disulfide so as to form a solution Reslllence, percents 50 containing 25 grams of polymer per liter of solution. Shore A hardness 9 56 Calibrations were based on deproteinized natural rubber ph i l mixture containing 65 percent M a complex as a reference material assuming that it contained 93 gin lan nne l retoi ie rgaction product and 35 percent of N,N'- percent cis and 2 percent 3,4-addition product. The 01s 11 en en 131111119. g g ,fi was measured at the 8.9 micron band and 3,4-addition Di-o-be izamidophenyl disulfide. 65 at the 11.25 micron band. In the presence of a high cis 2gggfg g gfigggfi figgfi f g ggg g ggfi 67 73 polyisoprene, trans is not detectable, since trans is meas- 254-2e0 (1956). flghis btilalueli'ts1 ti i lillumlfir of n egtwor i; chnagng ured at the 8.75 micron band. The raw cis and raw er unit volume 0 tu or. e 1g er 6 nu er, e r ghe rubber is crosslinked (vulcanized). 3,4 addition can be converted to normalized values by ASTM D412-6l'1. Scott Tensile Maohine L-G. Tests made changing each value proportionally so that their sum 80 F. I Y 7 ASTM D623 58. Methdd A Goodrich mexometer equals 100%. For polybutadiene, similar polymer solu lbs/sq. in. load, 0.175 inch stroke Testdspeciinenhilsrahnght tions were formed and the percent Of the total unsaturac l c l'nder 0.7 'nch in diame er an one inc 1g ms iis 'iM boats-59 (modified). Yerzley Oscillograph. Test t as i t accordmg to specimeln a! right circular cylinder 0.7 inch in diameter and t 6 following equation and 0011818126111; units.

1 1g Dug D67 6-59'11'. Shore durometer, type A. E The vulcanized rubber had good properties, as shown 6 =7 by the data. The rubbery polymers prepared by this process can be used for the manufacture of automobile and where e=extinction ffi i t (liters 1 1 centi truck tires. meterr E=extinction (log I /I); t=path length EXAMPLE III (centimeters; and c=concentration (moles double bond/ liter). The extinction was determined at the 10.35 micron n'Butyn.1thmm. was reacted Wlth benzyl alcohol using band and the extinction coefficient was 146 (liters-molsthe followmg reclpe centiineters" The percent of' the total .unsaturation Benzyl alcohol, mole 0.10 present as 1,2- (or vinyl) was calculated according to n-Butyllithium, mole 0.332 the above equation, using the 11.0 micron band and an extinction coefficient of 209 (liters-mols -centimeters- The percent of the total unsaturation present as cis 1,4- was obtained by subtracting the trans 1,4- and 1,2- (vinyl) determined according to the above procedure from the theoretical unsaturation, assuming one double bond per each C unit in the polymer.

One-tenth gram of polymer was placed in a wire cage made from 80 mesh screen and the cage was placed in 100 ml. of toluene contained in a wide-mouth, 4-ounce bottle. After standing at room temperature (approximately 77 F.) for 24 hours, the cage was removed and the solution was filtered through asulfur absorption tube of grade C porosity to remove any solid particles present. The resulting solution was run through a Medalia-type viscometer supported in a 77 F. bath. The viscometer was previously calibrated with toluene. The relative viscosity is the ratio of the viscosity of the polymer solution to that of toluene. The inherent viscosity is calculated by dividing the natural logarithm of the relative viscosity by the weight of the original sample (soluble portion).

Determination of gel was made along with the inherent viscosity determination. The wire cage was calibrated for toluene retention in order to correct the weight of swelled gel and to determine accurately the weight of dry gel.

The empty cage was immersed in toluene and then allowed to drain three minutes in a closed wide-mouth, two-ounce bottle. A piece of folded quarter-inch hardware cloth in the bottom of the bottle supported the cage with minimum contact. The bottle containing the cage was weighed to the nearest 0.02 gram during a minimum three-minute draining period after which the cage was withdrawn and the bottle again weighed to the nearest 0.02 gram. The difference in the two weighings is the weight of the cage plus the toluene retained by it, and by subtracting the weight of the empty cage from this value, the weight of toluene retention is found, i.e., the cage calibration. In the gel determination, after the cage containing the sample had stood for 24 hours in toluene, the cage was withdrawn from the bottle with the aid of forceps and placed in the two-ounce bottle. The same procedure was followed for determining the weight of swelled gel as was used for calibration of the cage. The weight of swelled gel was corrected by subtracting the cage calibration.

As will be apparent to those skilled in the art, various modifications can be made in this invention without departing from the spirit or scope thereof.

I claim:

1. A polymerization initiator which is the solid reaction product of an alkyllithium having up to 12 carbon atoms per molecule and a benzyl alcohol compound having the formula wherein R is selected from the group consisting of saturated aliphatic radicals and saturated cycloaliphatic radicals and m is an integer of O to 4, the total number of carbon atoms in the combined R- groups not exceeding 6 and at least one of the positions ortho to the CH OH group being unsubstituted.

2. An initiator composition which is the solid reaction product in a hydrocarbon diluent of n-butyllithiurn and benzyl alcohol.

3. A method of making a polymerization initiator which comprises contacting an alkyllithium having up to 12 carbon atoms per molecule with a benzyl alcohol compound having the formula Rm H which comprises reacting from 2 to 10 mole proportions of an alkyllithium having 2 to 6 carbon atoms per molecule with one mole proportion of a benzyl alcohol compound having the formula R... L'I

wherein R is selected from the group consisting of saturated aliphatic radicals and saturated cycloaliphatic radicals, m is an integer of 0 to 4, the total carbon atoms in the combined R groups not exceeding 6, at least one of the positions ortho to the.CH OH groups being unsubstituted, in a hydrocarbon diluent at a temperature in the range of m 200 F. and recovering the precipitate which forms.

5. The process of claim 4 wherein said alkyllithium is n-butyllithium and said benzyl alcohol compound is benzyl alcohol.

6. A polymerization process which comprises contacting a vinylidene-containing monomer under polymerization conditions in a hydrocarbon diluent with an initiator sparingly soluble in said diluent, said initiator being a solid reaction product of an alkyllithium having up to 12 carbon atoms per molecule with a benzyl alcohol compound having the formula Rm H wherein R is selected from the group consisting of saturated aliphatic radicals and saturated cycloaliphatic radicals and m is an integer of 0 to 4, the total number of carbon atoms in the combined R groups not exceeding 6 and at least one of the positions ortho to the CH' OH group being unsubstituted.

7. The process of claim 6 wherein said vinylidene-containing monomer is isoprene.

8. The process of claim 6 wherein said vinylidene-con- .taining monomer is butadiene.

Rm H

wherein R is selected from the group consisting of saturated aliphatic radicals and saturated eycloaliphatic radicals and m is an integer of 0 to 4, the total number of carbon atoms in the combined R groups not exceeding 6, at least one of the positions ortho to the CH OH groups being unsubstituted, and recovering a solid rubbery polymer.

No references cited.

JOSEPH L. SCHOFER,'Primary Examiner.

H. I. CANTOR, Assistant Examiner. 

1. A POLYMERIZATION INITIATOR WHICH IS THE SOLD REACTION PRODUCT OF AN ALKYLLITHIUM HAVING UP TO 12 CARBON ATOMS PER MOLECULE AND A BENZYL ALCOHOL COMPOUND HAVING THE FORMULA 